The production of elongated metal products is generally realized in a plant by a succession of steps. Normally, in a first step, metal scrap is provided as feed material to a furnace which heats up the scrap to reach the liquid status. Afterwards, continuous casting equipment is used to cool and solidify the liquid metal and to form a suitably sized strand.
Such a strand may then be cut to produce a suitably sized intermediate elongated product, typically a billet, to create feeding stock for a rolling mill. Normally, such feeding stock is then cooled down in cooling beds. Thereafter, a rolling mill is used to transform the feed stock, or billet, to a final elongated product, for instance rebar, available in different sizes which can be used in mechanical or construction industry. To obtain this result, the feed stock is pre-heated to a temperature which is suitable for entering the rolling mill where it is to be rolled by rolling equipment including multiple stands. By rolling the feed stock through these multiple stands, the feed stock is reduced to the desired cross section and shape. The elongated product resulting from the former rolling process is normally cut when it is still in a hot condition, then cooled down in a cooling bed, and finally cut at a commercial length and packed to be ready for delivery to a customer.
In the following, an endless operational mode of a plant for manufacturing elongated metal products will denote a plant arrangement wherein a direct, continuous link is established between a casting station and the rolling mill which is fed with the product of the casting procedure. In other words, the strand of intermediate product leaving the casting station is rolled by the rolling mill continuously along one casting line. Normally, when a plant operates in a fully endless mode, the continuous strand that is cast from the casting station along a corresponding casting line is fed to rolling mill, without being preliminarily cut into billets. In this case, the elongated intermediate product comes to effectively coincide with the strand leaving the casting station.
In the following, a semi-endless operational mode of a plant for manufacturing of elongated metal products denotes a plant arrangement, wherein the rolling mill is also fed with supplemental, normally preliminarily cut intermediate products which are originally external to the casting line directly linked to the rolling mill. Such intermediate products can be fed and inserted into the casting line which is directly connected to the rolling mill, for instance, by sourcing them from further casting lines which are not necessarily themselves aligned with and directly linked to the rolling mill.
When operating according to a so called endless mode, the rolling mill is arranged aligned with the strand produced by the billet caster. As a result, a manufacturing plant comprising direct casting and direct feeding of rolling mills, when dimensioned and conceived for operating in such endless mode, should ideally be as short as possible, in order to optimally utilize the internal heat of the just cast billets. Following this construction constraint, the space interposed between a first shear, normally located at the end of the caster, and an entrance into a customary intermediate billet heating device should be kept as short as possible. The compactness requirement remains naturally very desirable also when operating in a semi-endless mode.
Document WO 2012/013456 A2 discloses a plant comprising two casting lines producing two strands of intermediate product, such as billets. Such a plant provides a preliminary solution to the problem of better exploiting the hourly production rate of the steelmaking plant upstream, which is usually higher than the conventional production rate of rolling mills downstream. However, the layout of this plant is such that only one of two strands can be rolled to obtain a final product. By adopting a by-pass solution according to the concept disclosed in WO 2012/013456 A2, if there is at least a further strand available exiting from a caster, the additional billets resulting from such further strand are just transferred onto a conventional cooling bed. The billets which have been cooled down on such bed are then normally intended for direct sale and are not rolled according to an endless operational mode. Such a plant does therefore not provide optimal operational flexibility to be run either in a fully endless mode or in semi-endless mode.
In particular, such a plant does not allow fully exploiting the potentialities of a multi-strand caster in a way that the rolling mill throughput is actually optimized, for the production of as many rolled, final elongated products as desired.
On the other hand, existing plants which are able to operate in the so called semi-endless mode cannot ensure that the operation of inserting extra-billets into the casting line directly connected to the rolling mill happens in a cobble-free fashion and with full control over the billets' movements, both along the additional casting lines from which the supplemental billets are sourced and, especially, along the main casting line which is directly connected to the rolling mill.
None of the existing plants which can operate in a semi-endless mode and have a multi-strand caster effectively deal with the problem of avoiding that interferences are created between billets along the casting lines.
As a result of such lack of control, in current plants operating in a semi-endless mode, the workflow can be disrupted, in the feeding direction of the rolling mill as well as in the additional casting lines which are not aligned with the rolling mill.
Thus, a need exists in the prior art for an apparatus, and a corresponding method, for the production of elongated rolled products from a multiplicity of casting lines which encompasses a semi-endless operating mode, wherein the rolling mill output and the production rate of intermediate elongate products such as billets are optimized and happen in a cobble-free way, that is with no interferences between billets on one same casting line or across casting lines as a result of billet transfer.